Will the flow rate from an unvented cylinder be the same as the cold
water mains flow rate for eg,
if my cold water flow rate from mains is 31 liters per minute will the
hot water also be the same flow rate?
Do new cylinders need to have an insulation jacket?
Theoretically yes, but practically no because of additional resistance
of pipework. However, the starting flow rate is quite good so
shouldn't be a big issue.
They normally come with one in the form of foam encasing the cylinder
or a cylinder inside a cylinder with foam in between.
No, the extra pipework runs will restrict it somewhat, as will any water
softeners in place on the HW side.
Conversely if the kitchen tap is fed off a 15mm spur, and the tank and
bath off 22mm runs, you may get MORE..
They all come with em anyway.
31 litres/min at what pressure? Most unvented cylinders require a pressure
reducer which reduces flow. 22mm must be run from the stop to the cylinder
with no tee offs (he same with any main pressure DHW appliance, heat bank &
Don't buy an unvented cylinder. They require an annual service, which is
about £60. and they can do this:
cannot be DIY installed.
Buy a heat bank/thermal store. mains pressure at higher pressures, so higher
flows, no annual service charge, can be DIY fitted. Also the CH can be run
off it too. The boiler operates in a superior hydraulic environment too.
Greater benefits all around.
AVOID unvented cylinders.
Just checked, a 330 litre Dimplex mains pressure cylinder quotes
standing losses of less than 5kWh per 24h.
On other words, if you left it switched on all day on the electric
immersion, you'd use less electricity keeping it warm than running 3
lightbulbs or a 'typical' desktop computer.
There are quite tight limits for the heat losses on modern cylinders.
If it takes the immersion 1.5 hours to heat it from cold it'll take about
30 times that (45hours?) to go down. I think the rule is about 1W/litre.
Also, ideally you would want to run the cold supply to the bathroom(s)
off the pressure balanced outlet from the Pressure Reduction Valve. This
will allow reasonable control even with plain manual mixers.
My new bog-standard B&Q tank shows the following drops from 23:00 to 06:00 after
being heated - then left without any use:-
5 degrees C measured at the top
10 degrees C measured at approx 1/3 from the bottom.
i.e there is less volume of hot water available although what you get out
initially will still be a reasonable temperature.
An interesting side note of my measurents showed that if the heating was not
already in use (last October), the system reduced the temperature (by 2-3
degrees) of the lower portion of the cylinder initially (heat removed by coil to
pipe/boiler) and it took about 12 minutes for the temperature to return to its
I admit that my old boiler is not low-capacity and is several metres from the